Regarding photosemiconductor element sealing resin compositions, compositions including a bisphenol A type epoxy resin having excellent adhesiveness or mechanical strength; an epoxy resin which does not absorb UV, for example, a hydrogenated bisphenol A type epoxy resin or an alicyclic epoxy resin; and a curing agent as well as a curing catalyst, are frequently used. However, as the luminance and output power of LED elements are increasing, there is a problem of discoloration and cracking caused by the light, heat and the like emitted by the LED elements.
As a solution for these problems, resins produced by introducing an epoxy group into a silicone resin which gives a cured product that does not absorb UV and has flexibility, are known. For example, a silicone resin having one or more cyclic ether-containing groups such as a glycidyl group and an epoxycyclohexyl group (Patent Literature 1), a reaction product between an epoxyalkoxysilane and a silanol (Patent Literature 2), and a mixture combining an alicyclic epoxy-modified silicone resin and an alicyclic epoxy resin (Patent Literature 3), are known. However, since silicone resins have very high gas permeability compared to epoxy resins, as the silicone content increases, it becomes more difficult to use silicone resins for applications where low gas permeability is needed. Thus, an addition reaction type phenyl-based silicone resin composition has been disclosed as a resin composition having low gas permeability (Patent Literature 4); however, the resin composition is still not satisfactory in view of low gas permeability and adhesiveness.